Various publications, including patents, published applications, technical articles and scholarly articles are cited throughout the specification. Each of these cited publications is incorporated by reference herein, in its entirety.
Cytomegalovirus (CMV) is a herpes virus classified as being a member of the beta subfamily of herpesviridae. According to the Centers for Disease Control and Prevention, CMV infection is found fairly ubiquitously in the human population, with an estimated 40-80% of the United States adult population infected. The virus is spread primarily through bodily fluids, and is frequently passed from pregnant mothers to the fetus or newborn. In most individuals, CMV infection is latent, although virus activation can result in high fever, chills, fatigue, headaches, nausea, and splenomegaly.
Although most human CMV infections are asymptomatic, CMV infections in immunocompromised individuals, such as newborns, HIV-positive patients, allogeneic transplant patients and cancer patients, can be particularly problematic. CMV infection in such individuals can cause severe morbidity, including pneumonia, hepatitis, encephalitis, colitis, uveitis, retinitis, blindness, and neuropathy, among other deleterious conditions. In addition, CMV is a leading cause of birth defects (Britt WJ et al. 1996, Fields Virology, 3rd ed. 2493-2523). At present, there is no cure or preventive vaccine for CMV infection.
CMV infects various cells, including monocytes, macrophages, dendritic cells, neutrophils, endothelial cells, epithelial cells, fibroblasts, neurons, smooth muscle cells, hepatocytes, and stromal cells (Plachter B et al. 1996, Adv. Virus Res. 46:195-261). Infection of epithelial cells is significant because epithelial cells facilitate the spread of the virus within the host (Britt & Alford, 1996, supra). Infection of endothelial cells is significant because such cells are believed to be sites of human CMV persistence and latency, because endothelial cells are believed to be a gateway to leukocyte infection, because endothelial cells may facilitate mother to fetus/neonate transmission, and because infection of vascular endothelial cells is believed to contribute to various vascular pathologies, among other things (Jarvis M A et al. 2002, Curr. Opin. Microbiol. 5:403-7; Gerna G et al. 2002, J. Virol. 74:5629-38; Hengel et al. 2000, Trends Microbiol. 8:294-6; and, Patrone M et al. 2005, J. Virol. 79:8361-73).
In immunocompromised individuals, CMV infects multiple organ systems, replicating in all major cell types. Although clinical isolates replicate in a variety of cell types, laboratory strains, such as AD169 (Elek, S. D. & Stern, H.1974, Lancet 1, 1-5) and Towne (Plotkin, S. A., et al. 1975, Infect. Immun. 12, 521-527) replicate almost exclusively in fibroblasts (Hahn G et al. 2004, J. Virol. 78:10023-33). The restriction in tropism, which results from serial passage of the virus in fibroblasts, is a marker of attenuation (Gerna et al. 2002, supra). Mutations causing the loss of epithelial cell, endothelial cell, polymorphonuclear leukocyte, and dendritic cell tropism in human CMV laboratory strains have been mapped to three open reading frames (ORFs): UL128, UL130, and UL131 (Hahn et al. 2004, supra; Gerna, G., et al. 2005, J. Gen. Virol. 86, 275-284). Mutation of any one of these ORFs in the FIX clinical isolate of human CMV blocked endothelial cell tropism (Hahn et al. 2004, supra).
CMV particles contain three major glycoprotein complexes, all of which are required for human CMV infectivity. The gCI complex includes two molecules of the UL55-coded gB. Each 160-kDa monomer is cleaved to generate a 116-kDa surface unit linked by disulfide bonds to a 55-kDa transmembrane component. Some antibodies immunospecific for gB inhibit the attachment of virions to cells, whereas others block the fusion of infected cells, suggesting that the protein might execute multiple functions at the start of infection. Several cellular membrane proteins interact with gB, and these interactions likely facilitate entry and activate cellular signaling pathways. The gCII complex contains the UL 100-coded gM and UL73-coded gN, and it is the most abundant of the glycoprotein complexes. The complex binds to heparan sulfate proteoglycans, suggesting it might contribute to the initial interaction of the virion with the cell surface. It also could perform a structural role during virion assembly/envelopment, similar to the gM-gN complex found in some α-herpesviruses. The gCIII complex is comprised of UL75-coded gH, UL115-coded gL, and UL74-coded gO. All known herpesviruses encode gH-gL heterodimers (Spear, P. G. & Longnecker, R. 2003, J. Virol. 77, 10179-10185), which mediate fusion of the virion envelope with the cell membrane. Antibodies immunospecific for human CMV gH do not affect virus attachment but block penetration and cell-to-cell spread (Rasmussen, L. E. et al. 1984, Proc. Natl. Acad. Sci. USA 81, 876-880; Keay, S. & Baldwin, B. 1991, J. Virol. 65, 5124-5128). Expression of gH-gL in the absence of infection was sufficient to induce syncytia, and inclusion of gO in the assay did not enhance or block the fusion (Kinzler, E. R. & Compton, T. 2005, J. Virol. 79, 7827-7837). A gO-deficient mutant of AD169 shows a significant growth defect (Hobom, U. et al. 2000, J. Virol. 74, 7720-7729). Recently, it was reported that gH binds to integrin αvβ3 (Wang, X. et al. 2005, Nat. Med. 11, 515-521). However, the proteins encoded by UL131-UL128 heretofore have not been reported to be associated with any of the viral glyocoproteins.
There is a need for a CMV vaccine, and for effective means to control the spread and activation of the virus, particularly in immunocompromised individuals and pregnant women. There is also a need for methods to screen for antiviral compounds that inhibit cytomegalovirus infectivity.